This invention relates to a steering wheel provided with an air bag device arranged to protect an occupant at collision of a vehicle.
Currently, an air bag device is provided on a driver side to protect a driver at the collision of a vehicle such as an automobile. In general, this air bag device is mounted to a steering wheel. For example, an air bag is received within a cover member in a folded state, and disposed so that the cover member is positioned at a substantially central portion of an annular rim portion of the steering wheel so as to confront the driver.
When the large impact is applied at the collision of the vehicle, the air bag device senses the impact, generates a high pressure gas from an inflator, and supplies the high pressure gas into the air bag. Consequently, the air bag breaks the cover member by the inflation pressure, deploys the cover member outwardly, and rapidly expands and deploys on the front of the driver. Therefore, the driver is supported by the deployed air bag to absorb the impact on the driver. On a back side surface confronting the air bag, there are formed tear lines (breakable portions) for readily rapidly breaking the cover member and for rapidly expanding and deploying the air bag.
In a steering wheel with an air bag device of related art, an emblem and so on of a maker or manufacturer is provided on the front surface of the cover member of the air bag device which is disposed on a substantially central portion of the steering wheel, for enhancing the design and showing the brand. However, this emblem is harder than the cover member, and is difficult to break. Therefore, the tear lines are formed on the cover member at positions to avoid the position of emblem.
A patent document 1 (Japanese Patent Application Publication No. 2001-163156) discloses a cover member for an air bag device arranged to rapidly break the cover member in a case in which an emblem is mounted on a front surface of the cover member. As shown in a front view of FIG. 7, a cover member 51 of the patent document 1 includes a first tear line 53 which is not disposed at a is position corresponding to an emblem 52, and a second tear line 54 which is disposed at a position corresponding to emblem 52. Second tear line 54 is weaker than first tear line 53.
In cover member 51 of this patent document 1, first and second tear lines 53 and 54 can have shorter lengths, relative to a cover member having the tear lines disposed at positions to avoid the emblem. Moreover, it is possible to rapidly break the weak tear line 54 by the inflation pressure. Therefore, the breakaway of first tear line 53 is promoted by the breakaway of second tear line 54 so as to improve the speed-up of the deployment of the air bag.
In recent years, the emblem mounted on the surface of the cover member tends to increase in the size for enhancing the decoration effect. That is, letters and figures used as the emblem increase in the size for effectively appealing a vehicle name and a maker name. Moreover, the emblem has the relatively larger size, with respect to the cover member. Accordingly, it is possible to show the cover member to the small size by the visual effect, and thereby to suppress the oppression of the driver.
A patent document 2 (U.S. Patent Application Publication No. 2004/174002 A1 (corresponding to Japanese Patent Application Publication No. 2004-268911)) discloses a cover member for an air bag device which is arranged to smoothly break the cover member in a case in which a large emblem is provided on a front surface of the cover member. This cover member includes tear lines disposed across the emblem. The emblem itself is formed with tear lines located at positions corresponding to the positions of the tear lines of the cover member to promote the breakaway. Accordingly, even when the large emblem is provided on the surface of the cover member, it is possible to smoothly break along the tear lines of the cover member and the tear lines of the emblem when the cover member receives the inflation pressure of the air bag.
FIG. 7 shows cover member 51 of the patent document 1. This cover member 51 is broken along tear lines 53 and 54 at the deployment of the air bag, so as to form an upper door portion 55, and lower left and right door portions 56a and 56b. Moreover, door portions 55, 56a and 56b are pivoted, respectively, to a plurality of spaces defined (surrounded) by a circular rim portion of the steering wheel, a boss portion disposed at a substantially central portion of the rim portion, and spoke portions each connecting the rim portion and the boss portion. In this case, the upper space defined within the steering wheel serves as an opening through which the driver can see a meter.
However, this cover member 51 breaks along first and second tear lines 53 and 54 at the deployment of the air bag, and upper door portion 55 is pivoted to the upper space. This upper door portion 55 is mounted with an emblem 52. Accordingly, in a case in which emblem 52 has a large size, upper door portion 55 becomes large in size. When upper door portion 55 is pivoted, upper door portion 55 widely blocks the upper region for seeing the meter. This is not preferred because the driver becomes difficult to see the meter. Accordingly, in cover member 51 of patent document 1, it is difficult to increase the size of emblem 52.
On the other hand, the cover member of the patent document 2 is formed with the tear lines, and moreover the emblem is formed with the tear lines. However, in the cover member of the patent document 2, it is necessary to appropriately form the breakable portions so as to surely break the hard emblem, and to mount the emblem to the door portions of the cover member so as not to release the broken emblem. Therefore, material and shapes of the cover member and the emblem are limited. Moreover, it requires the high technology as to the design, the process control and the quality control. Consequently, the manufacturing cost is increased.
By the way, the air bag device is mounted to the steering wheel so as to appropriately ensure the safety of the driver by the deployment of the folded air bag, on the assumption that the driver sits on the driver's seat in a normal driving posture. Moreover, it is also required to decrease the pressure of the air bag to the driver at the deployment of the air bag to ensure the safety of the driver, in a case in which that the driver is in an out-of-position that the driver is nearer to the steering wheel relative to the normal posture.
Therefore, in cover member 51 of the patent document 1 shown in FIG. 7 and the cover member of the patent document 2, the door portions are formed by the breakaway of the tear lines at the inflation of the air bag, pivoted, respectively, to the spaces formed within the steering wheel, and pushed into those spaces.
Accordingly, even when the air bag is inflated while the driver is in the out-of-position, the upper and lower door portions of the air bag are pushed into the spaces of the steering wheel. Therefore, it is possible to escape the part of the air bag hit on the driver from the spaces of the steering wheel in the forward direction of the vehicle. Consequently, it is possible to suppress the force of the air bag which pushes the driver in the rearward direction, and to ensure the safety of the driver.
However, in the air bag device, it is required to further improve the safety of the driver who is in the out-of-position to safely surely protect the driver in any situations. This technology is still being developed positively.